Williams alleged the trips aboard Melgen’s private jet were for parties with prostitutes. Menendez is divorced and adult prostitution is not illegal in the Dominican Republican. FBI agents are investigating Williams’ allegations and raided Melgen’s office the week before last, apparently seeking evidence of Medicare fraud.

The Wall Street Journal reported in 2010 that Menendez had directly and strongly urged the Federal Reserve to approve a deal that would have benefitted a deeply troubled New Jersey bank where eight of its directors had contributed to his campaigns.

In 2006, the U.S. district attorney in New Jersey, now Republican Gov. Chris Christie, investigated complaints that Menendez broke conflict-of-interest rules by renting property to a nonprofit agency that received federal funds. Menendez countered that the anti-poverty agency received U.S. funds for years before he went to Congress, Christie himself was later accused of political bias and no charges were ever filed.

Republicans also have accused him of steering business to a former top congressional aide who later founded a lobbying firm. He has denied the complaints and said the staffer earned the contracts because she’s a good lobbyist.

Menendez has flatly denied the allegations made by Williams in emails to some news media and the watchdog Citizens for Responsibility and Ethics in Washington (CREW) — which turned over the tips to the FBI but is now questioning their veracity.

“Williams” waited until Menendez was seeking reelection last year to make his charges public and never spoke by phone with the FBI, “so those two facts combined to seriously undermine his credibility,” CREW Executive Director Melanie Sloan told CNN.

Menendez’s office did not respond to a request for comments for this story, but many who know him have strongly defended him.

“Senator Menendez has always been straightforward and honorable,” said Florida Republican Rep. Mario Diaz-Balart.

“He’s one of the most principled people I know,” added Mauricio Claver-Carone, executive director of the pro-sanctions U.S. Cuba Democracy Political Action Committee in Washington.

His Senate Web page calls his “a quintessential American story” — high school senior class president, school board member at 20, a law degree from the state university and, at 32, mayor of Union City, sometimes called Havana-on-the-Hudson for its large Cuban population.

Born in New York City, he is the youngest of the three children of a Cuban couple who migrated to the United States in 1953. His father committed suicide when Menendez was 23, according to some biographies.

He launched his political careers as a protégé of Union City Mayor William “Billy” Musto, but in 1982 he testified in a federal corruption trial that sent Musto to prison for three years. Menendez told reporters he wore a bulletproof vest during the trial.

Menendez served as mayor of Union City from 1986 until 1992, when he was elected to the U.S. House of Representatives. He was appointed to the Senate in early 2006 when Jon Corzine gave up his seat to become governor of New Jersey. Menendez then won new six-year terms in 2006 and in 2012. He is the sixth Hispanic elected to the Senate.

He divorced Jane Jacobsen, a former Union City teacher, in 2005 after nearly 30 years of marriage. They have two adult children, Robert Jr. and Alicia.

From early in his political career Menendez was very close to the Cuban exiles who began jamming Union City after Fidel Castro’s guerrillas seized power in 1959, and since reaching Congress he has worked hand in hand with other Cuban-American members to maintain economic sanctions on the island.

“He is one of the most effective advocates for a hard-line against the Castro regime that I have ever encountered,” said Cardenas, a Colombian American who previously served in Washington as a representative of the Cuban American National Foundation and as a top official of the U.S. Agency for International Development. Cardenas volunteered that he had donated to Menendez’s latest campaign.

Menendez is one of three Cuban-American Democrats in Congress, along with Reps. Albio Sires of New Jersey and Joe Garcia of South Florida. The four other Cuban Americans in Congress are Republicans — Sen. Marco Rubio of Florida and Ted Cruz of Texas, and South Florida Reps. Ros-Lehtinen and Diaz-Balart.